The present invention relates to amphiphilic polymer networks and methods for their preparation. The networks comprise the reaction product of hydrophobic crosslinking agents and hydrophilic monomers. The present invention is more particularly related to an amphiphilic polymer network comprising the reaction product of multi-arm multi-telechelic polyisobutylene stars as hydrophobic crosslinking agents and acrylate or methacrylate hydrophilic monomers. Applications include implantable biological devices comprising the amphiphilic networks that are capable of encapsulating and immunoisolating biologically active moieties, such as cells, from the immune response of a host individual.
Many medical deficiencies and diseases result from the inability of cells to produce normal biologically active moieties. Many of these deficiencies can be remedied by implanting the needed biologically active moieties or pharmacological agents into the individual having the deficiency. A well known disease that can be remedied by implanting biological material or a pharmacological agent is Type I diabetes mellitus, wherein the production of insulin by pancreatic Langerhans islet cells is substantially deficient, impaired, or nonexistent.
Encapsulating human islet cells or tissues within a biologically compatible device followed by implanting the device into a host individual has been proposed as a means for providing insulin to an individual with Type I diabetes. However, an individual""s immune response frequently attacks foreign biological material such as cells, tissues, and organs. And the response severely limits the effectiveness of methods that involve implanting foreign biological material.
Porcine pancreatic islet cells can produce insulin, and their supply is much greater than that of human pancreatic islet cells. Therefore, transplanting porcine islet cells, if effectively immunoisolated from the normal immunological response of a human, would be of great benefit to a vast number of individuals with type I diabetes.
Amphiphilic polymer networks can serve as a means to encapsulate and thereby immunoisolate implantable biologically active moieties. An amphiphilic polymer network comprises hydrophilic and hydrophobic monomers and polymers that can swell in both polar and nonpolar solvents. Amphiphilic polymer networks have been disclosed in the prior art: U.S. Pat. Nos. 4,486,572 and 4,942,204 to Kennedy, U.S. Pat. No. 5,073,381 to Ivxc3xa1n, Kennedy and Mackey, and in Keszler and Kennedy, Journal of Macromolecular Science, Chemistry Edition, Vol. A21, No. 3, pages 319-334 (1984).
U.S. Pat. No. 4,486,572 to Kennedy discloses the synthesis of styryl-telechelic polyisobutylene and amphiphilic networks comprising the copolymerization product of the styryl-telechelic polyisobutylene with vinyl acetate or N-vinyl-2-pyrollidone.
U.S. Pat. No 4,942,204 to Kennedy discloses an amphiphilic copolymer network swellable in water or n-heptane but insoluble in either, comprising the product of the reaction of an acrylate or methacrylate of dialkylaminoalkyl with a hydrophobic bifunctional acryloyl or methacryloyl capped polyelofin. The preferred embodiment disclosed is an amphiphilic network having been synthesized by free-radical copolymerization of linear hydrophobic acrylate (A-PIB-A) or methacrylate (MA-PIB-MA) capped polyisobutylenes with 2-(dimethylamino)ethyl methacrylate (DMAEMA).
U.S. Pat. No. 5,073,381 to Ivan et al., a continuation-in-part of U.S. Pat. No. 4,942,204, discloses various amphiphilic copolymer networks that are swellable in water or n-heptane that comprise the reaction product of a hydrophobic linear acryloyl or methacryloyl capped polyolefin and a hydrophilic polyacrylate or polymethacrylate, such as N,N-dimethylacrylamide (DMAAm) and 2-hydroxyethyl methylmethacrylate (HEMA).
U.S. Pat. No. 4,085,168 to Milkovich et al. describes chemically joined, phase-separated self-cured hydrophilic thermoplastic graft copolymers that are copolymers of at least one hydrophilic (water soluble) ethylenically unsaturated monomer or mixture thereof and at least one copolymerizable hydrophobic macromolecular monomer having an end group that is copolymerizable with the hydrophilic monomer. The resulting copolymer is a graft copolymer characterized as having a comb-type structure consisting of a hydrophilic polymer backbone with hydrophobic polymer side chains bonded thereto. The side chains are disclosed as being bonded to the hydrophilic polymer at only one end of the side chain, so that no network results.
In addition, U.S. Pat. No. 5,807,944 to Hirt et al. discloses an amphiphilic segmented copolymer of controlled morphology comprising at least one oxygen permeable polymer segment and at least one ion permeable polymer segment, wherein the oxygen permeable segments and the ion permeable segments are linked together through a non-hydrolyzable bond. The oxygen permeable polymer segments are selected from polysiloxanes, perfluoroalkyl ethers, polysulfones, and other unsaturated polymers. The ion permeable polymers are selected from cyclic imino ethers, vinyl ethers, cyclic ethers, including epoxides, cyclic unsaturated ethers, N-substituted aziridines, xcex2-lactones, xcex2-lactanes, ketene acetates, vinyl acetates and phosphoranes.
U.S. Pat. No. 5,800,828 to Dionne et al. discloses immunoisolatory vehicles having a core and a surrounding jacket that is capable of secreting a biologically active product or of providing a biological function to a patient, said vehicle being permselective, biocompatible, and having a molecular weight cutoff permitting passage of molecules between the patient and the core of the vehicle, and wherein the jacket is selected from polyacrylonitrile-polyvinylchloride, polyacrylonitrile, poly(methyl methacrylate), poly(vinyl difluoride), polyolefins, polysulfones and celluloses.
U.S. Pat. No. 5,844,056 to Kennedy et al. discloses methods for the synthesis of multi-arm star polymers comprising polyisobutylene arms connected to a well-defined calixarene core. The core comprises multifunctional calix[n]arene where n is an integer from 4 to 16, and methods are also disclosed for synthesizing the polyisobutylene arms stemming from the core. This patent is hereby incorporated by reference.
U.S. patent application having Ser. No. 09/433,660 discloses amphiphilic networks comprising the reaction product of telechelic three-arm polyisobutylene star hydrophobic crosslinking agents and acrylate or methacrylate hydrophilic monomers, and implantable biological devices comprising the amphiphilic networks that are capable of encapsulating and immunoisolating biologically active moieties, such as cells, from the immune response of a host individual. This application is hereby incorporated by reference.
The amphiphilic networks taught in the prior art, while suitable for biomedical applications, have tensile strengths that are rather low, namely less than or equal to about 0.5 MPa. It is therefore desirable in the art to develop amphiphilic networks, and implantable biological devices comprising the amphiphilic networks that have superior immunoisolatory properties, superior mechanical properties, biocompatability, and exhibit excellent biostability when placed into a host individual for extended periods of time.
It is, therefore, an object of the present invention to provide an amphiphilic network.
It is another object of the present invention to provide an amphiphilic network, as above, that can encase biologically active moieties.
It is another object of the present invention to provide an amphiphilic network, as above, that is immunoisolatory, i.e., networks that can selectively regulate the passage of biological material into, out of, and through the network.
It is another object of the present invention to provide an amphiphilic network, as above, that is biocompatible with a host individual.
It is another object of the present invention to provide an amphiphilic network, as above, that exhibits excellent biostability once implanted into a host individual.
It is another object of the present invention to provide an amphiphilic network, as above, that is hemocompatible with a host individual.
It is another object of the present invention to provide an amphiphilic network, as above, that is readily sterilizable.
It is another object of the present invention to provide an amphiphilic network, as above, that is easily retrievable from a host individual after implantation in an individual.
It is another object of the present invention to provide an amphiphilic network, as above, that exhibits excellent mechanical properties.
It is another object of the present invention to provide an amphiphilic network, as above, that is swellable in both hydrophilic and hydrophobic solvents.
It is another object of the present invention to provide an implantable biological device that can encase biologically active substances and immunoisolate said biologically active substances from the immunological response of a host individual.
It is another object of the present invention to provide a method for treating of Type I diabetes mellitus.
One or more of these or other objects, together with the advantages thereof over the amphiphilic networks and biological devices comprising amphiphilic networks of the existing art, which shall become apparent from the specification that follows, are accomplished by the invention as hereinafter described and claimed.
In general, the present invention provides an amphiphilic network comprising the reaction product of hydrophobic crosslinking agents and hydrophilic monomers, wherein said hydrophobic crosslinking agents are multi-arm multi-telechelic polyisobutylene stars having acrylate or methacrylate end caps and represented by formula (I): 
wherein R1 is polyisobutylene represented by formula (II): 
wherein x is the degree of polymerization of said polyisobutylene;
wherein R2 is either H or CH3;
wherein A is a moiety that connects R1 to said acrylate or methacrylate end caps;
wherein n is an integer from 4 to 16; and
wherein said hydrophilic monomers are derived from an acrylate selected from
the group consisting of formulas (III), (IV) and (V): 
wherein R3 is hydrogen or methyl, R4 is an alkylene group having from about 2 to about 4 carbon atoms, and R5 and R6 may be the same or different and each is hydrogen or an alkyl radical having 1 to about 4 carbon atoms.
The present invention also provides a method of forming an amphiphilic network comprising the steps of:
copolymerizing and crosslinking hydrophilic monomers, wherein said hydrophilic monomers are derived from an acrylate selected from the group consisting of formulas (III), (IV) and (V): 
wherein R3 is hydrogen or methyl, R4 is an alkylene group having from about 2 to about 4 carbon atoms, and R5 and R6 may be the same or different and each is hydrogen or an alkyl radical having 1 to about 4 carbon atoms; and
with hydrophobic crosslinking agents, wherein said hydrophobic crosslinking agents are multi-arm multi-telechelic polyisobutylene stars having acrylate or methacrylate end caps and represented by formula (I): 
wherein R1 is polyisobutylene represented by formula (II): 
wherein x is the degree of polymerization of said polyisobutylene;
wherein R2 is either H or CH3;
wherein A is a moiety that connects R1 to said acrylate or methacrylate end caps; and
wherein n is an integer from 4 to 16.
The present invention further provides an implantable biological device that is capable of encapsulating biologically active moieties, and immunoisolating said moieties from an immune response of a host individual, said device comprising an amphiphilic network comprising the reaction product of hydrophobic crosslinking agents and hydrophilic monomers, wherein said hydrophobic crosslinking agents are multi-arm multi-telechelic polyisobutylene stars having acrylate or methacrylate end caps and represented by formula (I): 
wherein R1 is polyisobutylene represented by formula (II): 
wherein x is the degree of polymerization of said polyisobutylene;
wherein R2 is either H or CH3;
wherein A is a moiety that connects R1 to said acrylate or methacrylate end caps;
wherein n is an integer from 4 to 16; and
wherein said hydrophilic monomers are derived from an acrylate selected from the group consisting of formulas (III), (IV) and (V): 
wherein R3 is hydrogen or methyl, R4 is an alkylene group having from about 2 to about 4 carbon atoms, and R5 and R6 may be the same or different and each is hydrogen or an alkyl radical having 1 to about 4 carbon atoms.
The present invention further provides a method for producing an implantable biological device that encapsulates and immunoisolates biologically active moieties and can be implanted into a host individual, comprising the steps of forming an amphiphilic network comprising the reaction product of hydrophobic crosslinking agents and hydrophilic monomers, wherein said hydrophobic crosslinking agents are multi-arm multi-telechelic polyisobutylene stars having acrylate or methacrylate end caps and represented by formula (I): 
wherein R1 is polyisobutylene represented by formula (II): 
wherein x is the degree of polymerization of said polyisobutylene;
wherein R2 is either H or CH3;
wherein A is a moiety that connects R1 to said acrylate or methacrylate end caps;
wherein n is an integer from 4 to 16; and
wherein said hydrophilic monomers are derived from an acrylate selected from the group consisting of formulas (III), (IV) and (V): 
wherein R3 is hydrogen or methyl, R4 is an alkylene group having from about 2 to about 4 carbon atoms, and R5 and R6 may be the same or different and each is hydrogen or an alkyl radical having 1 to about 4 carbon atoms; and forming said amphiphilic network into a desired three-dimensional geometric shape.
The present invention further provides a method for treating Type I diabetes in a diabetic host individual comprising the steps of providing an amphiphilic network comprising the reaction product of hydrophobic crosslinking agents and hydrophilic monomers, wherein said hydrophobic crosslinking agents are multi-arm multi-telechelic polyisobutylene stars having acrylate or methacrylate end caps and represented by formula (I): 
wherein R1 is polyisobutylene represented by formula (II): 
wherein x is the degree of polymerization of said polyisobutylene;
wherein R2 is either H or CH3;
wherein A is a moiety that connects R1 to said acrylate or methacrylate end caps;
wherein n is an integer from 4 to 16; and
wherein said hydrophilic monomers are derived from an acrylate selected from the group consisting of formulas (III), (IV) and (V): 
wherein R3 is hydrogen or methyl, R4 is an alkylene group having from about 2 to about 4 carbon atoms, and R5 and R6 may be the same or different and each is hydrogen or an alkyl radical having 1 to about 4 carbon atoms; forming said amphiphilic network into an elongated tubular device; encasing a sufficient amount of islet of pancreatic cells within said tubular device, wherein said tubular device is capable of immunoisolating said encased islet cells upon implantation into a diabetic-host individual; implanting said device into said diabetic-host individual; and allowing said implanted tubular device to remain implanted in said diabetic-host individual for a time sufficient to normalize the blood glucose level in said diabetic-host individual.